Surface modified pigments and non-aqueous inks therewith

ABSTRACT

A method for preparing a surface modified organic pigment includes the steps of a) reacting the organic pigment in an aromatic hydrocarbon solvent with a surface modifying reagent to form a surface modified organic pigment; and b) washing and drying the surface modified organic pigment; wherein the surface modifying reagent is represented by Formula (I): 
     
       
         
         
             
             
         
       
     
     wherein,
 
X is selected from the group consisting of O, S and N—R3; Y is selected from the group consisting of —O and NR4; R1 to R4 are each independently selected from the group consisting of hydrogen, an alkyl group, an alkenyl group, an alkynyl group, a -aralkyl group, an alkaryl group, and an aryl group and s heteroaryl group; with the proviso that when Y—R1 is different from OH that at least one of R2 to R4 is substituted by at least one functional group having a pKa between 2.5 and 9.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage application ofPCT/EP2012/073145, filed Nov. 21, 2012. This application claims thebenefit of U.S. Provisional Application No. 61/577,100, filed Dec. 19,2011, which is incorporated by reference herein in its entirety. Inaddition, this application claims the benefit of European ApplicationNo. 11193407.1, filed Dec. 14, 2011, which is also incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a new class of surface modified organicpigments, a process for their preparation and non-aqueous inks includingat least one such surface modified pigment.

2. Description of the Related Art

In industrial ink jet systems, there is a constant demand for increasedprinting speeds in combination with high image quality. This requires anexcellent dispersion quality and stability of the inks in order toguarantee continuous printing without production loss due to nozzle orengine failures. The new print heads designed for increasing printingspeed only operate with very low viscous inkjet inks which generallyexhibit inferior shelf life stability. In addition, the reduction ofpigment particle size for image quality also tends to result in morecritical shelf life stability.

Polymeric dispersants are substances for promoting the formation andstabilization of a dispersion of pigment particles in a dispersionmedium. They typically contain in one part of the molecule so-calledanchor groups, which adsorb onto the pigments to be dispersed. In aspatially separate part of the molecule, polymeric dispersants havepolymer chains compatible with the dispersion medium, thus stabilizingthe pigment particles in the dispersion medium.

In aqueous pigment dispersions, the polymeric dispersants generallycontain hydrophobic anchor groups exhibiting a high affinity for thepigment surface and hydrophilic polymer chains for stabilizing thepigments in the aqueous dispersion medium. Thermally stable non-aqueousdispersions with submicron particles are much more difficult to prepare,especially for pigments having a non-polar surface.

Several methods to improve the dispersibility of organic pigments aredisclosed in The Chemistry of Inkjet Inks. Edited by MAGDASSI, Shlomo.Singapore: World Scientific Publishing Co., 2010. p. 111-119.

Often commercially available polymeric dispersants are used as generalpurpose dispersants for all pigment types. However, it is known in theart that several pigments cannot be milled down to the required particlesize for high end ink jet applications using only general purposedispersants. In a first approach to optimize the dispersion quality ofthese pigments, dedicated dispersants have been designed, containingstructural moieties, having a structural similarity with the pigment tobe dispersed. Such dispersant designs have been disclosed in WO2007/089859 (CABOT), WO 2007/006634 (AGFA), WO 2007/006635 (AGFA), WO2007/006636 (AGFA), WO 2007/006637 (AGFA), WO 2007/006638 (AGFA) and WO2007/006639 (AGFA). However this approach, though very effective,requires the design of a dedicated dispersant for each class ofpigments, leading to high costs making this approach less attractivefrom an economical and industrial point of view.

In a second approach, so called dispersion synergists have beendeveloped to improve the dispersibility of specific pigments incombination with general purpose dispersants. Dispersion synergists areespecially useful to disperse pigments with a hydrophobic surface in anon-aqueous dispersion medium by modifying the pigment surface to ahydrophilic surface. Several dispersion synergists have beencommercialized, such as Solsperse™ 5000 from Lubrizol. WO 2007/060254(AGFA) discloses quinacridone derivatives having carboxylic acid groupsfor modifying the surface of quinacridone pigments. Other dispersionsynergists are disclosed in WO 2007/060255 (AGFA), WO 2007/060259(AGFA), WO 2007/060264 (AGFA), WO 2007/060265 (AGFA) and WO 2007/060265(AGFA). As dispersion synergists generally show a certain molecularsimilarity with the pigments to be dispersed, this approach alsorequires the development of a specific dispersion synergist for eachpigment class, leading again to a high additional cost and aneconomically less attractive option.

In a third approach, the pigment surface is modified by direct chemicalreaction introducing polar or acid groups on the pigment surface, whichshould enhance the interaction with the dispersants used in the millingprocess.

Diazonium technology has been successfully used both on carbon black anddifferent organic pigments to introduce functional groups as disclosedin U.S. Pat. No. 5,851,280 (CABOT) and U.S. Pat. No. 5,837,045 (CABOT).However, this technology requires an aqueous environment, making itdifficult to extend the technology to solvent based and UV based inks.

Surface sulfonation has been disclosed in U.S. Pat. No. 3,528,840(HUBER), US 2003134938 (DAINICHISEIKA COLOR) and EP 2316886 A (AGFA).Sulfonation leads to highly acidic pigment surfaces, which areincompatible with cationic radiation curable formulations or vinyl ethercontaining free radical radiation curable formulations, unless specificprecautions are taken. Vinyl ethers, such as vinylether acrylatesdisclosed by EP 997508 A (AGFA), are of special interest for preparinglow viscous radiation curable ink jet inks suitable for the new printheads designed for increasing printing speed.

Therefore, it would be advantageous to design carboxylation technologyfor surface modification of organic pigments, making the modifiedpigments compatible with vinyl ether containing radiation curableformulations by design.

Surface carboxylation through hydrolysis has been disclosed in WO2008/034472 (AGFA) and WO 2004/094534 (CABOT). However, this technologyis restricted to organic pigments comprising hydrolysable groups intheir structure. Several industrially interesting pigment classes cannotbe surface modified using this technology.

U.S. Pat. No. 6,264,733 (CIBA) discloses surface modification with aformaldehyde precursor in combination with aromatic carboxylic acids ina strong acidic medium. Strong acids are not easy to remove frompigments filter cakes by washing. Traces of strong acid catalysts renderthe pigment incompatible with vinyl ether containing radiation curableformulations.

U.S. Pat. No. 6,831,194 (COLUMBIAN CHEMICALS) uses cyclic anhydrides incombination with Lewis acids to introduce gamma keto carboxylic acids onthe pigment surface. Also Lewis acids have to be removed to the lasttrace to render the pigment compatible with vinyl ether containingradiation curable formulations.

Hence there is still a need for carboxylation technology, applicable ona broad range of pigments, without the need for significant amounts ofstrong acids or Lewis acids as catalysts.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, it has beensurprisingly found that a wide range of pigments could be carboxylatedusing specific acids, such as glyoxylic acid, pyruvic acid,2-oxobutanoic acid and phenyl glyoxylic acid, without the need forstrong acids or Lewis acids as catalysts.

Preferred embodiments of the present invention provide a new class ofsurface modified organic pigments, having an improved dispersion qualityand stability, especially in non-aqueous (inkjet) inks.

Other preferred embodiments of the present invention provide a simplesynthetic process for the preparation of the surface modified organicpigments.

Even further preferred embodiments of the present invention providehighly stable radiation curable (inkjet) inks including at least onesurface modified organic pigment according to the preferred embodimentsdescribed above, especially vinyl ether containing radiation curable(inkjet) inks.

These and other advantages and benefits will become apparent in thedescription hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Definitions

The term “mixed crystal”, which is synonymous for “solid solution”, asused in disclosing the present invention, means a solid, homogeneousmixture of two or more constituents, which may vary in compositionbetween certain limits and remain homogeneous. In a solid solution, themolecules of the components enter into the same crystal lattice,usually, but not always, that of one of the components. The x-raydiffraction pattern of the resulting crystalline solid is characteristicof that solid and can be clearly differentiated from the pattern of aphysical mixture of the same components in the same proportion asindividual pigments. In such physical mixtures, the x-ray pattern ofeach of the components can be distinguished, and the disappearance ofmany of these lines is one of the criteria of the formation of solidsolutions.

The term “C.I.” is used in disclosing the present application as anabbreviation for Colour Index.

Methods for Preparing Surface Modified Organic Pigments

Method for preparing a surface modified organic pigment comprising thesteps of:

a) reacting an organic pigment in an aromatic hydrocarbon solvent with asurface modifying reagent to form a surface modified organic pigment;andb) washing and drying the surface modified organic pigment; wherein thesurface modifying reagent is represented by Formula (I):

wherein,X is selected from the group consisting of O, S and N—R3;Y is selected from the group consisting of O, NR4;R1 to R4 are each independently selected from the group consisting ofhydrogen, a substituted or unsubstituted alkyl group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted alkynylgroup, a substituted or unsubstituted aralkyl group, a substituted orunsubstituted alkaryl group, a substituted or unsubstituted aryl groupand a substituted or unsubstituted heteroaryl group;with the proviso that when Y—R1 is different from OH that at least oneof R2 to R4 is substituted by at least one functional group having a pKabetween 2.5 and 9.

Suitable functional groups having a pKa between 2.5 and 9 are carboxylicacids, acyl sulfonamides, sulfonamides, aminocarbonyl sulfoximides,N-cyano-sulfonamide, cyanamide tetrazoles, phenols substituted withelectron withdrawing groups, oximes, imidazolidinones, barbituric acidderivatives, heterocyclic thiols, sulfonamides substituted withheterocyclic rings, heterocyclic aromatic rings, aromatic rings and uricacid derivatives without being limited thereto.

In a preferred embodiment the functional group having a pKa between 2.5and 9 is a carboxylic acid group.

To determine whether the functional group has a pKa between 2.5 and 9, awater soluble compound comprising the functional group is used tomeasure the pKa according to the following method. The pKa is determinedusing a combined glass electrode (electrolyte: KCl 3M in water). Thepotentiometric titration is performed at 25° C. in a thermostaticvessel. The electrode is calibrated at 25° C. using Merck buffers of pH4, pH 7 and pH 10. An 0.01M aqueous solution of the compound isprepared. This solution is titrated under N2 (nitrogen) atmosphere usinga 0.01 M HCl or 0.01 M NaOH titrant. During the titration the solutionis stirred using a magnetic stirrer. The Henderson-Hasselbach equationis simplified at the half equivalence point to pH=pKa. This halfequivalence point is determined using the first derivative.

The substituted or unsubstituted alkyl group is preferably a C₂ toC₆-alkyl group.

The substituted or unsubstituted alkenyl group is preferably a C₂ toC₆-alkenyl group.

The substituted or unsubstituted alkynyl group is preferably a C₂ toC₆-alkynyl group.

The substituted or unsubstituted aralkyl group is preferably phenylgroup or naphthyl group including one, two, three or more C₁ to C₆-alkylgroups.

The substituted or unsubstituted alkaryl group is preferably a C₁ toC₆-alkyl group including a phenyl group or naphthyl group.

The substituted or unsubstituted aryl group is preferably a phenyl groupor naphthyl group

The substituted or unsubstituted heteroaryl group is preferably a five-or six-membered ring substituted by one, two or three oxygen atoms,nitrogen atoms, sulphur atoms, selenium atoms or combinations thereof.

The substituted alkyl group, the substituted alkenyl group, thesubstituted alkynyl group, the substituted aralkyl group, thesubstituted alkaryl group, the substituted aryl and the substitutedheteroaryl group are preferably substituted by one or more substituentsselected from the group consisting of methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl and tertiary-butyl, —Cl, —Br, —I, —OH, —CNand —NO₂.

In a more preferred embodiment, the surface modifying reagent isrepresented by Formula (II):

wherein R2 is defined as above for Formula (I).

In a preferred embodiment, X represents O.

In a preferred embodiment, R2 is selected from the group consisting ofhydrogen, a substituted or unsubstituted alkyl group and a substitutedor unsubstituted aryl group.

In a more preferred embodiment, R2 is selected from the group consistingof hydrogen and a substituted or unsubstituted alkyl group.

In the most preferred embodiment, R2 represents hydrogen.

Preferred surface modifying reagents are selected from the groupconsisting of glyoxylic acid, pyruvic acid, 2-oxobutanoic acid andphenyl glyoxylic acid. Suitable surface modifying reagents including asubstituted or unsubstituted aryl group include phenylglyoxylic acid and4-cyanophenylglyoxylic acid.

The surface modified organic pigments according to the present inventionare preferably prepared by reacting the surface of the organic pigmentwith a surface modifying reagent according to Formula (I) or (II) undercatalytic acidic conditions.

Catalytic acidic conditions are defined as conditions where the molarratio of acid catalyst over surface modifying agent is lower then 0.5.In a preferred embodiment, the ratio is lower the 0.4. In a morepreferred embodiment, the ratio is lower then 0.3. In a furtherpreferred embodiment the acid catalyst is a Brönsted acid having a pKalower then 2, lower then 1 being more preferred. In another preferredembodiment, no extra acid catalyst is used.

The method for preparing a surface modified organic pigment preferablyuses as reaction medium an aromatic hydrocarbon solvent preferablyselected from the group consisting of toluene, o-xylene, m-xylene,p-xylene and mixtures thereof.

The surface modified organic pigment is preferably washed using anaromatic hydrocarbon solvent optionally in combination with a ketone,such as acetone or butanone. The aromatic hydrocarbon solvent forwashing the pigment is preferably the same aromatic hydrocarbon solventused as reaction medium.

In a preferred embodiment, the organic pigment is selected from thegroup consisting of quinacridone pigments, diketopyrrolopyrrolepigments, quinolonoquinolone pigments, dioxazine pigments,aminoanthraquinone pigments, indanthrone pigments,bisbenzimidazobenzophenanthroline dione pigments and mixed crystalsthereof.

In a preferred embodiment, the quinacridone pigment is selected from thegroup consisting of C.I. Pigment Red 122, 192, 202, 207, 209, C.IPigment Violet 19 and mixed crystals thereof. Most preferably, thequinacridone pigment is C.I. Pigment Red 122, C.I. Pigment Red 192, C.I.Pigment Red 202, C.I Pigment Violet 19 and a mixed crystal thereof.

In a preferred embodiment, the diketopyrrolopyrrole pigment (DPP) isselected from the group consisting of C.I. Pigment Orange 71, C.I.Pigment Red 254, Pigment Red 255 and a mixed crystal thereof.

In another preferred embodiment, the organic pigment is aDPP/quinacridone solid solution.

In a preferred embodiment, the quinolonoquinolone pigment is selectedfrom the group consisting of C.I. Pigment Yellow 218, C.I. PigmentYellow 220, C.I. Pigment Yellow 221 and mixed crystals thereof.

In a preferred embodiment, the dioxazine pigment is C.I. Pigment Violet23.

In a preferred embodiment, the aminoanthraquinone pigment is C.I.Pigment Red 177.

In a preferred embodiment, the indanthrone pigment is C.I. Pigment Blue60.

In a preferred embodiment, the bisbenzimidazobenzophenanthroline dionepigments is represented by Formula (PB043):

Surface Modified Organic Pigments

Preferred embodiments of the present invention include the surfacemodified organic pigment obtained by above described method forpreparing a surface modified organic pigment.

A surface modified organic pigment according to a preferred embodimentof the present invention includes at least one functional groupaccording to Formula (III) attached to its surface:

wherein,the dashed line represents a covalent bond to one of the pigmentmolecules at the pigment surface;X is selected from the group consisting of OR5, SR6, NR3R7 and halogen;Y is selected from the group consisting of O, NR4;R1 to R4 are independently selected from the group consisting ofhydrogen, a substituted or unsubstituted alkyl group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted alkynylgroup, a substituted or unsubstituted aralkyl group, a substituted orunsubstituted alkaryl group, a substituted or unsubstituted aryl group,a substituted or unsubstituted heteroaryl group;R5 to R7 are independently selected from the group consisting ofhydrogen, a substituted or unsubstituted alkyl group, a substituted orunsubstituted alkenyl group, a substituted or unsubstituted alkynylgroup, a substituted or unsubstituted aralkyl group, a substituted orunsubstituted alkaryl group, a substituted or unsubstituted aryl groupand a substituted or unsubstituted heteroaryl group and a substituted orunsubstituted acyl group;any one of R1 to R7 may represent the necessary atoms to form a five toeight membered ring with one of the other groups selected from R1 to R7;with the proviso that when Y—R1 is different from OH that at least oneof R2 to R7 is substituted by at least one functional group having a pKabetween 2.5 and 9.

Suitable functional groups having a pKa between 2.5 and 9 are carboxylicacids, acyl sulfonamides, sulfonamides, aminocarbonyl sulfoximides,N-cyano-sulfonamide, cyanamide tetrazoles, phenols substituted withelectron withdrawing groups, oximes, imidazolidinones, barbituric acidderivatives, heterocyclic thiols, sulfonamides substituted withheterocyclic rings and uric acid derivatives without being limitedthereto.

In a preferred embodiment the functional group having a pKa between 2.5and 9 is a carboxylic acid group.

In a more preferred embodiment, Y represents O and R1 is hydrogen.

In an even further preferred embodiment, X is selected from the groupconsisting of OR5 and NR3R7, with OR5 being particularly preferred.

In the most preferred embodiment X is a hydroxyl group.

In a further preferred embodiment R2 is selected from the groupconsisting of hydrogen, a substituted or unsubstituted alkyl group and asubstituted or unsubstituted aryl group; more preferably R2 is selectedfrom the group consisting of hydrogen and a substituted or unsubstitutedalkyl group and most preferably R2 is hydrogen.

The substituted or unsubstituted alkyl group is preferably a C₁ toC₆-alkyl group.

The substituted or unsubstituted alkenyl group is preferably a C₁ toC₆-alkenyl group.

The substituted or unsubstituted alkynyl group is preferably a C₁ toC₆-alkynyl group.

The substituted or unsubstituted aralkyl group is preferably phenylgroup or naphthyl group including one, two, three or more C₁ to C₆-alkylgroups.

The substituted or unsubstituted alkaryl group is preferably a C₁ toC₆-alkyl group including a phenyl group or naphthyl group.

The substituted or unsubstituted aryl group is preferably a phenyl groupor naphthyl group

The substituted or unsubstituted heteroaryl group is preferably a five-or six-membered ring substituted by one, two or three oxygen atoms,nitrogen atoms, sulphur atoms, selenium atoms or combinations thereof.

The substituted or unsubstituted acyl group is preferably a C₁ toC₆-acyl group.

The substituted alkyl group, the substituted alkenyl group, thesubstituted alkynyl group, the substituted aralkyl group, thesubstituted alkaryl group, the substituted aryl, the substitutedheteroaryl group and the substituted acyl group are preferablysubstituted by one or more substituents selected from the groupconsisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl andtertiary-butyl, —Cl, —Br, —I, —OH, —CN and —NO₂.

In a preferred embodiment, the one of the pigment molecules at thepigment surface is selected from the group consisting of quinacridone,diketopyrrolopyrrole, quinolonoquinolone, dioxazine, aminoanthraquinone,indanthrone and bisbenzimidazobenzophenanthroline dione.

In a preferred embodiment, the one of the pigment molecules at thepigment surface is a quinacridone selected from the group consisting ofC.I. Pigment Red 122, 192, 202, 207, 209, C.I Pigment Violet 19. Mostpreferably, the quinacridoneis C.I. Pigment Red 122, C.I. Pigment Red192, C.I. Pigment Red 202 and C.I Pigment Violet 19.

In a preferred embodiment, the one of the pigment molecules at thepigment surface is a diketopyrrolopyrrole (DPP) selected from the groupconsisting of C.I. Pigment Orange 71, C.I. Pigment Red 254 and PigmentRed 255.

In a preferred embodiment, the one of the pigment molecules at thepigment surface is a quinolonoquinolone pigment selected from the groupconsisting of C.I. Pigment Yellow 218, C.I. Pigment Yellow 220 and C.I.Pigment Yellow 221.

In a preferred embodiment, the dioxazine pigment molecule at the pigmentsurface is C.I. Pigment Violet 23.

In a preferred embodiment, the aminoanthraquinone pigment molecule atthe pigment surface is C.I. Pigment Red 177.

In a preferred embodiment, the indanthrone pigment molecule at thepigment surface is C.I. Pigment Blue 60.

In a preferred embodiment, the bisbenzimidazobenzophenanthroline dionepigment molecule at the pigment surface is represented by Formula(PB043):

The surface modified pigment is preferably present in the range of 0.05to 20%, more preferably in the range of 0.1 to 10% by weight and mostpreferably in the range of 1 to 6% by weight, each based on the totalweight of the pigment dispersion or (inkjet) ink.

Non-Aqueous Pigment Dispersions

The surface modified organic pigments according to the present inventioncan be used in water based, solvent based, oil based and radiationcurable formulations and inks. However, the surface modified organicpigments can be advantageously dispersed in non-aqueous pigmentdispersions and (inkjet) inks for improving the dispersion quality andstability.

The non-aqueous pigment dispersion or (inkjet) ink includes preferablyat least a non-aqueous dispersion medium, a polymeric dispersant and atleast one surface modified organic pigment according to the presentinvention. In a preferred embodiment, the non-aqueous pigment dispersionor (inkjet) ink is curable by UV radiation or e-beam.

The surface modified organic pigments according to the present inventionare especially suitable for preparing highly stable radiation curable(inkjet) inks including a polymerizable compound having at least onevinyl ether group. These radiation curable (inkjet) inks can be freeradical curable or cationically curable inks. The cationically curableink includes at least one vinyl ether and preferably one or moreepoxides or oxetanes.

In a preferred embodiment, the radiation curable ink is a free radicalradiation curable ink including a polymerizable compound having at leastone vinyl ether group.

Preferred examples of the vinyl ether compound include monovinyl ethercompounds such as ethyl vinyl ether, n-propyl vinyl ether, isopropylvinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecyl vinylether, cyclohexyl vinyl ether, phenyl vinyl ether, hydroxyethyl vinylether, hydroxybutyl vinyl ether, 2-ethylhexyl vinyl ether,cyclohexanedimethanol monovinyl ether, isopropenyl ether-O-propylenecarbonate, dodecyl vinyl ether, diethyleneglycol monovinyl ether,octadecyl vinyl ether; and the like.

Preferred examples of the vinyl ether compound include multifunctionalvinylethers, such as divinyl ethers and trivinyl ethers.

Preferred divinyl ethers including ethylene glycol divinylether,diethylene glycol divinylether, polyethylene glycol divinylether,propylene glycol divinylether, butylene glycol divinylether, hexanedioldivinylether, bisphenol A alkyleneoxide divinylethers, and bisphenol Falkyleneoxide divinylethers.

Preferred multifunctional vinyl ethers having more than two vinyl ethergroups include trimethylolethane trivinylether, trimethylolpropanetrivinylether, ditrimethyrollpropane tetravinylether, glyceroltrivinylether, pentaerythritol tetravinylether, dipentaerythritolpentavinylether, dipentaerythritol hexavinylether, ethyleneoxide adductsof trimethylolpropane trivinylether, propyleneoxide adducts oftrimethylolpropane trivinylether, ethyleneoxide adducts ofditrimethyrollpropane tetravinylether, propyleneoxide adducts ofditrimethyrollpropane tetravinylether, ethyleneoxide adducts ofpentaerythritol tetravinylether, propyleneoxide adducts ofpentaerythritol tetravinylether, ethyleneoxide adducts ofdipentaerythritol hexavinylether, and propyleneoxide adducts ofdipentaerythritol hexavinylether, and the like.

Of these vinyl ether compounds, divinyl ether compounds and trivinylether compounds are preferred, and divinyl ether compounds areparticularly preferred, in view of curability, adhesiveness and surfacehardness. The vinyl ether compounds may be used by solely one kind, oras a suitable combination of two or more kinds.

In a radiation curable (inkjet) ink, the divinyl ether compounds andtrivinyl ether compounds are preferably present in an amount of at least20 wt %, more preferably at least 30 wt % and most preferably at least40 wt % based upon the total weight of the radiation curable compositionused in the radiation curable (inkjet) ink.

In a more preferred embodiment, the free radical radiation curable inkincludes at least one vinyl ether methacrylate or vinyl ether acrylate,an acrylate being particularly preferred.

The vinylether (meth)acrylate is preferably represented by Formula (V):

wherein,R¹ represents hydrogen or a methyl group,L represents a linking group comprising at least one carbon atom,X represents O, S or NR² wherein R² has the same meaning as R¹;when X═NR², L and R² may form together a ring system, and n and mindependently represent a value from 1 to 5.

In a preferred embodiment, the compound according to Formula (V) has R²representing hydrogen, X representing 0, and n representing a valueof 1. The value of m is preferably 1, 2 or 3. L preferably comprises 2,3 or 4 carbon atoms.

Preferred vinylether (meth)acrylates are those disclosed in U.S. Pat.No. 6,310,115 (AGFA). Particularly preferred compounds are2-(2-vinyloxyethoxy)ethyl(meth)acrylate, most preferably the compound is2-(2-vinyloxyethoxy)ethyl acrylate. Other suitable vinylether(meth)acrylates are those disclosed in columns 3 and 4 of U.S. Pat. No.6,767,980 (NIPPON CATALYTIC).

A single compound or a mixture of vinylether (meth)acrylates may beused.

In a radiation curable (inkjet) ink, the vinylether acrylate ispreferably present in an amount of at least 20 wt %, more preferably atleast 30 wt % and most preferably at least 40 wt % based upon the totalweight of the radiation curable composition used in the radiationcurable (inkjet) ink.

The radiation curable (inkjet) ink is preferably a non-aqueous (inkjet)ink. The term “non-aqueous” refers to a liquid carrier which shouldcontain no water. However sometimes a small amount, generally less than5 wt % of water based on the total weight of the ink, can be present.This water was not intentionally added but came into the formulation viaother components as a contamination, such as for example polar organicsolvents. Higher amounts of water than 5 wt % tend to make thenon-aqueous (inkjet) inks instable, preferably the water content is lessthan 1 wt % based on the total weight dispersion medium and mostpreferably no water at all is present.

The radiation curable (inkjet) ink preferably contains a dispersant,more preferably a polymeric dispersant, for dispersing the pigment. Thecurable ink may contain a dispersion synergist to improve the dispersionquality of the ink. A mixture of dispersion synergists may be used tofurther improve dispersion stability.

The viscosity of the radiation curable inkjet ink is preferably smallerthan 30 mPa·s, more preferably smaller than 15 mPa·s, and mostpreferably between 1 and 10 mPa·s at 25° C. and at a shear rate of 100s⁻¹. The viscosity of the inkjet ink at the jetting temperature ispreferably smaller than 30 mPa·s, more preferably smaller than 15 mPa·s,and most preferably between 1 and 10 mPa·s at a shear rate of 100 s⁻¹and a jetting temperature between 10 and 70° C.

The radiation curable (inkjet) ink may further also contain at least oneinhibitor.

The non-aqueous (inkjet) ink forms preferably part of a non-aqueous CMYK(inkjet) ink set. The non-aqueous CMYK (inkjet) ink set may also beextended with extra inks such as red, green, blue, and/or orange tofurther enlarge the colour gamut of the image. The CMYK (inkjet) ink setmay also be extended by the combination of full density and lightdensity inks of both colour inks and/or black inks to improve the imagequality by lowered graininess.

Non-Aqueous Dispersion Media

The dispersion medium used in the pigment dispersion according to apreferred embodiment of the present invention is a non-aqueous liquid.The dispersion medium may consist of organic solvent(s), oil(s) orpolymerizable compounds or combinations thereof.

Suitable organic solvents include alcohols, aromatic hydrocarbons,ketones, esters, aliphatic hydrocarbons, higher fatty acids, carbitols,cellosolves, higher fatty acid esters. Suitable alcohols includemethanol, ethanol, propanol and 1-butanol, 1-pentanol, 2-butanol,t.-butanol. Suitable aromatic hydrocarbons include toluene, and xylene.Suitable ketones include methyl ethyl ketone, methyl isobutyl ketone,2,4-pentanedione and hexafluoroacetone. Also glycol, glycolethers,N-methylpyrrolidone, N,N-dimethylacetamid, N, N-dimethylformamid may beused.

Preferred examples of organic solvents are disclosed in [0133] to [0146]of EP 1857510 A (AGFA GRAPHICS).

If the pigment dispersion is a curable (inkjet) ink, organic solvent(s)are preferably fully replaced by one or more monomers and/or oligomersto obtain the liquid dispersion medium. Sometimes, it can beadvantageous to add a small amount of an organic solvent to improve thedissolution of the dispersant. The content of organic solvent should belower than 20 wt %, more preferably lower than 5 wt % based on the totalweight of the (inkjet) ink and most preferably the curable pigmentdispersion or ink doesn't include any organic solvent.

For oil based pigment dispersions and (inkjet) inks the dispersionmedium can be any suitable oil including aromatic oils, paraffinic oils,extracted paraffinic oils, naphthenic oils, extracted napthenic oils,hydrotreated light or heavy oils, vegetable oils and derivatives andmixtures thereof. Paraffinic oils can be normal paraffin types (octaneand higher alkanes), isoparaffins (isooctane and higher iso-alkanes) andcycloparaffins (cyclooctane and higher cyclo-alkanes) and mixtures ofparaffin oils.

Suitable examples of oils are disclosed in [0151] to of EP 1857510 A(AGFA GRAPHICS).

Monomers and Oligomers

The monomers and oligomers used in radiation curable pigment dispersionsand inks, especially for food packaging applications, are preferablypurified compounds having no or almost no impurities, more particularlyno toxic or carcinogenic impurities. The impurities are usuallyderivative compounds obtained during synthesis of the polymerizablecompound. Sometimes, however, some compounds may be added deliberatelyto pure polymerizable compounds in harmless amounts, for example,polymerization inhibitors or stabilizers.

Any monomer or oligomer capable of free radical polymerization may beused as polymerizable compound. A combination of monomers, oligomersand/or prepolymers may also be used. The monomers, oligomers and/orprepolymers may possess different degrees of functionality, and amixture including combinations of mono-, di-, tri- and higherfunctionality monomers, oligomers and/or prepolymers may be used. Theviscosity of the radiation curable compositions and inks can be adjustedby varying the ratio between the monomers and oligomers.

Particularly preferred monomers and oligomers are those listed in [0106]to [0115] in EP 1911814 A (AGFA GRAPHICS).

Polymeric Dispersants

Typical polymeric dispersants are copolymers of two monomers but maycontain three, four, five or even more monomers. The properties ofpolymeric dispersants depend on both the nature of the monomers andtheir distribution in the polymer. Suitable copolymeric dispersants havethe following polymer compositions:

-   -   statistically polymerized monomers (e.g. monomers A and B        polymerized into ABBAABAB);    -   alternating polymerized monomers (e.g. monomers A and B        polymerized into ABABABAB);    -   gradient (tapered) polymerized monomers (e.g. monomers A and B        polymerized into AAABAABBABBB);    -   block copolymers (e.g. monomers A and B polymerized into        AAAAABBBBBB) wherein the block length of each of the blocks (2,        3, 4, 5 or even more) is important for the dispersion capability        of the polymeric dispersant;    -   graft copolymers (graft copolymers consist of a polymeric        backbone with polymeric side chains attached to the backbone);        and    -   mixed forms of these polymers, e.g. blocky gradient copolymers.

Suitable polymeric dispersants are listed in the section on“Dispersants”, more specifically [0064] to [0070] and [0074] to [0077],in EP 1911814 A (AGFA GRAPHICS) incorporated herein as a specificreference.

The polymeric dispersant has preferably a number average molecularweight Mn between 500 and 30000, more preferably between 1500 and 10000.

The polymeric dispersant has preferably a weight average molecularweight Mw smaller than 100,000, more preferably smaller than 50,000 andmost preferably smaller than 30,000.

The polymeric dispersant has preferably a polydispersity PD smaller than2, more preferably smaller than 1.75 and most preferably smaller than1.5.

Commercial examples of polymeric dispersants are the following:

-   -   DISPERBYK™ dispersants available from BYK CHEMIE GMBH;    -   SOLSPERSE™ dispersants available from NOVEON;    -   TEGO™ DISPERS™ dispersants from EVONIK;    -   EDAPLAN™ dispersants from MÜNZING CHEMIE;    -   ETHACRYL™ dispersants from LYONDELL;    -   GANEX™ dispersants from ISP;    -   DISPEX™ and EFKA™ dispersants from CIBA SPECIALTY CHEMICALS INC;    -   DISPONER™ dispersants from DEUCHEM; and    -   JONCRYL™ dispersants from JOHNSON POLYMER.

Particularly preferred polymeric dispersants include Solsperse™dispersants from NOVEON, Efka™ dispersants from CIBA SPECIALTY CHEMICALSINC and Disperbyk™ dispersants from BYK CHEMIE GMBH. Particularlypreferred dispersants are Solsperse™ 32000, 35000 and 39000 dispersantsfrom NOVEON.

The polymeric dispersant is preferably used in an amount of 2 to 600 wt%, more preferably 5 to 200 wt %, most preferably 50 to 90 wt % based onthe weight of the pigment.

Initiators

The curable (inkjet) ink preferably contains an initiator for initiatingthe polymerization reaction. The initiator can be a thermal initiator,but is preferably a photo-initiator. The photo-initiator requires lessenergy to activate than the monomers, oligomers and/or prepolymers toform the polymer. The photo-initiator suitable for use in the curable(inkjet) ink may be a Norrish type I initiator, a Norrish type IIinitiator or a photo-acid generator.

Thermal initiator(s) suitable for use in the curable (inkjet) inkinclude tert-amyl peroxybenzoate, 4,4-azobis(4-cyanovaleric acid),1,1′-azobis(cyclohexanecarbonitrile), 2,2′-azobisisobutyronitrile(AIBN), benzoyl peroxide, 2,2-bis(tert-butylperoxy)butane,1,1-bis(tert-butylperoxy)cyclohexane,1,1-bis(tert-butylperoxy)cyclohexane,2,5-bis(tert-butylperoxy)-2,5-dimethylhexane,2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne,bis(1-(tert-butylperoxy)-1-methylethyl)benzene,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, tert-butylhydroperoxide, tert-butyl peracetate, tert-butyl peroxide, tert-butylperoxybenzoate, tert-butylperoxy isopropyl carbonate, cumenehydroperoxide, cyclohexanone peroxide, dicumyl peroxide, lauroylperoxide, 2,4-pentanedione peroxide, peracetic acid and potassiumpersulfate.

The photo-initiator or photo-initiator system absorbs light and isresponsible for the production of initiating species, such as freeradicals and cations. Free radicals and cations are high-energy speciesthat induce polymerization of monomers, oligomers and polymers and withpolyfunctional monomers and oligomers thereby also inducingcross-linking.

Irradiation with actinic radiation may be realized in two steps bychanging wavelength or intensity. In such cases it is preferred to use 2types of photo-initiator together.

A combination of different types of initiator, for example, aphoto-initiator and a thermal initiator can also be used.

Suitable photo-initiators are disclosed in CRIVELLO, J.V., et al. VOLUMEIII: Photoinitiators for Free Radical Cationic. 2nd edition. Edited byBRADLEY, G. London, UK: John Wiley and Sons Ltd, 1998. p. 287-294.

Specific examples of photo-initiators may include, but are not limitedto, the following compounds or combinations thereof: benzophenone andsubstituted benzophenones, 1-hydroxycyclohexyl phenyl ketone,thioxanthones such as isopropylthioxanthone,2-hydroxy-2-methyl-1-phenylpropan-1-one,2-benzyl-2-dimethylamino-(4-morpholinophenyl) butan-1-one, benzildimethylketal, bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphineoxide, 2,4,6trimethylbenzoyldiphenylphosphine oxide,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,2,2-dimethoxy-1,2-diphenylethan-1-one or 5,7-diiodo-3-butoxy-6-fluorone,diphenyliodonium fluoride and triphenylsulfonium hexafluophosphate.

The curable (inkjet) ink may contain a photo-initiator system containingone or more photo-initiators and one or more sensitizers that transferenergy to the photo-initiator(s). Suitable sensitizers includephotoreducible xanthene, fluorene, benzoxanthene, benzothioxanthene,thiazine, oxazine, coumarin, pyronine, porphyrin, acridine, azo, diazo,cyanine, merocyanine, diarylmethyl, triarylmethyl, anthraquinone,phenylenediamine, benzimidazole, fluorochrome, quinoline, tetrazole,naphthol, benzidine, rhodamine, indigo and/or indanthrene dyes. Theamount of the sensitizer is in general from 0.01 to 15 wt %, preferablyfrom 0.05 to 5 wt %, based in each case on the total weight of thecurable (inkjet) ink.

The photoinitiator is preferably a free radical initiator. A freeradical photoinitiator is a chemical compound that initiates apolymerization of monomers and oligomers when exposed to actinicradiation by the formation of a free radical.

Two types of free radical photoinitiators can be distinguished and usedin the pigment dispersion or ink in a preferred embodiment of thepresent invention. A Norrish Type I initiator is an initiator whichcleaves after excitation, yielding the initiating radical immediately. ANorrish type II-initiator is a photoinitiator which is activated byactinic radiation and forms free radicals by hydrogen abstraction from asecond compound that becomes the actual initiating free radical. Thissecond compound is called a polymerization synergist or co-initiator.Both type I and type II photoinitiators can be used in a preferredembodiment of the present invention, alone or in combination.

Preferred examples of photo-initiators may include, but are not limitedto, the following compounds or combinations thereof: benzophenone andsubstituted benzophenones, 1-hydroxycyclohexyl phenyl ketone,thioxanthones such as isopropylthioxanthone,2-hydroxy-2-methyl-1-phenylpropan-1-one,2-benzyl-2-dimethylamino-(4-morpholinophenyl) butan-1-one, benzildimethylketal, bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphineoxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,2,2-dimethoxy-1,2-diphenylethan-1-one or 5,7-diiodo-3-butoxy-6-fluorone,diphenyliodonium fluoride and triphenylsulfonium hexafluophosphate.

Suitable commercial photo-initiators include Irgacure™ 184, Irgacure™500, Irgacure™ 907, Irgacure™ 369, Irgacure™ 1700, Irgacure™ 651,Irgacure™ 819, Irgacure™ 1000, Irgacure™ 1300, Irgacure™ 1870, Darocur™1173, Darocur™ 2959, Darocur™ 4265 and Darocur™ ITX available from CIBASPECIALTY CHEMICALS, Lucerin™ TPO available from BASF AG, Esacure™KT046, Esacure™ KIP150, Esacure™ KT37 and Esacure™ EDB available fromLAMBERTI, H-Nu™ 470 and H-Nu™ 470X available from SPECTRA GROUP Ltd.

Suitable cationic photo-initiators include compounds, which form aproticacids or Bronstead acids upon exposure to ultraviolet and/or visiblelight sufficient to initiate polymerization. The photo-initiator usedmay be a single compound, a mixture of two or more active compounds, ora combination of two or more different compounds, i.e. co-initiators.Non-limiting examples of suitable cationic photo-initiators arearyldiazonium salts, diaryliodonium salts, triarylsulphonium salts,triarylselenonium salts and the like.

However for safety reasons, in particular for food packagingapplications, the photoinitiator is preferably a so-called diffusionhindered photoinitiator. A diffusion hindered photoinitiator is aphotoinitiator which exhibits a much lower mobility in a cured layer ofthe curable liquid or ink than a monofunctional photoinitiator, such asbenzophenone. Several methods can be used to lower the mobility of thephotoinitiator. One way is to increase the molecular weight of thephotoinitiator so that the diffusion speed is reduced, e.g. difunctionalphotoinitiators or polymeric photoinitiators. Another way is to increaseits reactivity so that it is built into the polymerizing network, e.g.multifunctional photoinitiators and polymerizable photoinitiators. Thediffusion hindered photoinitiator is preferably selected from the groupconsisting of non-polymeric di- or multifunctional photoinitiators,oligomeric or polymeric photoinitiators and polymerizablephotoinitiators. Non-polymeric di- or multifunctional photoinitiatorsare considered to have a molecular weight between 300 and 900 Dalton.Non-polymerizable monofunctional photoinitiators with a molecular weightin that range are not diffusion hindered photoinitiators. Mostpreferably the diffusion hindered photoinitiator is a polymerizableinitiator.

A suitable diffusion hindered photoinitiator may contain one or morephotoinitiating functional groups derived from a Norrish typeI-photoinitiator selected from the group consisting of benzoinethers,benzil ketals, α,α-dialkoxyacetophenones, α-hydroxyalkylphenones,α-aminoalkylphenones, acylphosphine oxides, acylphosphine sulfides,α-haloketones, α-halosulfones and phenylglyoxalates.

A suitable diffusion hindered photoinitiator may contain one or morephotoinitiating functional groups derived from a Norrish typeII-initiator selected from the group consisting of benzophenones,thioxanthones, 1,2-diketones and anthraquinones.

Suitable diffusion hindered photoinitiators are also those disclosed inEP 2053101 A (AGFA GRAPHICS) in paragraphs [0074] and [0075] fordifunctional and multifunctional photoinitiators, in paragraphs [0077]to [0080] for polymeric photoinitiators and in paragraphs [0081] to[0083] for polymerizable photoinitiators.

A preferred amount of photoinitiator is 0-50 wt %, more preferably0.1-20 wt %, and most preferably 0.3-15 wt % of the total weight of thecurable pigment dispersion or (inkjet) ink.

In order to increase the photosensitivity further, the curable pigmentdispersion or ink may additionally contain co-initiators. Suitableexamples of co-initiators can be categorized in 3 groups:

(1) tertiary aliphatic amines such as methyldiethanolamine,dimethylethanolamine, triethanolamine, triethylamine andN-methylmorpholine;(2) aromatic amines such as amylparadimethylaminobenzoate,2-n-butoxyethyl-4-(dimethylamino)benzoate,2-(dimethylamino)ethylbenzoate, ethyl-4-(dimethylamino)benzoate, and2-ethylhexyl-4-(dimethylamino)benzoate; and(3) (meth)acrylated amines such as dialkylamino alkyl(meth)acrylates(e.g., diethylaminoethylacrylate) or N-morpholinoalkyl-(meth)acrylates(e.g., N-morpholinoethyl-acrylate).The preferred co-initiators are aminobenzoates.

When one or more co-initiators are included into the curable pigmentdispersion or (inkjet) ink according to a preferred embodiment of thepresent invention, preferably these co-initiators are diffusion hinderedfor safety reasons, in particular for food packaging applications.

A diffusion hindered co-initiator is preferably selected from the groupconsisting of non-polymeric di- or multifunctional co-initiators,oligomeric or polymeric co-initiators and polymerizable co-initiators.More preferably the diffusion hindered co-initiator is selected from thegroup consisting of polymeric co-initiators and polymerizableco-initiators. Most preferably the diffusion hindered co-initiator is apolymerizable co-initiator.

A preferred diffusion hindered co-initiator is a polymeric co-initiatorhaving a dendritic polymeric architecture, more preferably ahyperbranched polymeric architecture. Preferred hyperbranched polymericco-initiators are those disclosed in US 2006014848 (AGFA) incorporatedherein as a specific reference.

A more preferred diffusion hindered co-initiator is one or morepolymerizable co-initiators. In a preferred embodiment the polymerizableco-initiator comprises at least one (meth)acrylate group, mostpreferably at least one acrylate group.

Preferred diffusion hindered co-initiators are the polymerizableco-initiators disclosed in EP 2053101 A (AGFA) in paragraphs [0088] and[0097].

The curable pigment dispersion or (inkjet) ink preferably includes theco-initiator in an amount of 0.1 to 50 wt %, more preferably in anamount of 0.5 to 25 wt %, most preferably in an amount of 1 to 10 wt %of the total weight of the ink.

Polymerization Inhibitors

The curable (inkjet) ink may contain a polymerization inhibitor.Suitable polymerization inhibitors include phenol type antioxidants,hindered amine light stabilizers, phosphor type antioxidants,hydroquinone monomethyl ether commonly used in (meth)acrylate monomers,and hydroquinone, t-butylcatechol, pyrogallol may also be used.

Suitable commercial inhibitors are, for example, Sumilizer™ GA-80,Sumilizer™ GM and Sumilizer™ GS produced by Sumitomo Chemical Co. Ltd.;Genorad™ 16, Genorad™ 18 and Genorad™ 20 from Rahn AG; Irgastab™ UV10and Irgastab™ UV22, Tinuvin™ 460 and CGS20 from Ciba SpecialtyChemicals; Floorstab™ UV range (UV-1, UV-2, UV-5 and UV-8) fromKromachem Ltd, Additol™ S range (S100, S110, S120 and S130) from CytecSurface Specialties.

Since excessive addition of these polymerization inhibitors will lowerthe ink sensitivity to curing, it is preferred that the amount capableof preventing polymerization is determined prior to blending. The amountof a polymerization inhibitor is preferably lower than 2 wt % of thetotal pigment dispersion or (inkjet) ink.

Binders

Non-aqueous pigment dispersions and (inkjet) inks based on organicsolvents or oils preferably include a binder resin. The binder functionsas a viscosity controlling agent and also provides fixability relativeto a polymeric resin substrate, e.g. a polyvinyl chloride substrate,also called vinyl substrate. The binder must be selected to have a goodsolubility in the solvents or oils.

Suitable examples of binder resins include acrylic resins, modifiedacrylic resins, styrene acrylic resins, acrylic copolymers, acrylateresins, aldehyde resins, rosins, rosin esters, modified rosins andmodified rosin resins, acetyl polymers, acetal resins such as polyvinylbutyral, ketone resins, phenolic resins and modified phenolic resins,maleic resins and modified maleic resins, terpene resins, polyesterresins, polyamide resins, polyurethane resins, epoxy resins, vinylresins, vinyl chloride-vinyl acetate copolymer resins, cellulose typeresins such as nitro cellulose, cellulose acetopropionate and celluloseacetate butyrate, and vinyl toluene-α-methylstylene copolymer resin.These binders may be used alone or in a mixture thereof. The binder ispreferably a film-forming thermoplastic resin.

The amount of binder resin in a pigment dispersion or (inkjet) ink ispreferably in the range of 0.1 to 30 wt %, more preferably 1 to 20 wt %,most preferably 2 to 10 wt % based on the total weight of the pigmentdispersion or (inkjet) ink.

Surfactants

The pigment dispersion or (inkjet) ink may contain at least onesurfactant. The surfactant(s) can be anionic, cationic, non-ionic, orzwitter-ionic and are usually added in a total quantity less than 20 wt%, preferably in a total quantity less than 3 wt % based on the totalweight of the pigment dispersion or (inkjet) ink.

Suitable surfactants include fluorinated surfactants, fatty acid salts,ester salts of a higher alcohol, alkylbenzene sulphonate salts,sulphosuccinate ester salts and phosphate ester salts of a higheralcohol (for example, sodium dodecylbenzenesulphonate and sodiumdioctylsulphosuccinate), ethylene oxide adducts of a higher alcohol,ethylene oxide adducts of an alkylphenol, ethylene oxide adducts of apolyhydric alcohol fatty acid ester, and acetylene glycol and ethyleneoxide adducts thereof (for example, polyoxyethylene nonylphenyl ether,and SURFYNOL™ 104, 104H, 440, 465 and TG available from AIR PRODUCTS &CHEMICALS INC.).

For non-aqueous (inkjet) inks preferred surfactants are preferablyselected from fluoro surfactants (such as fluorinated hydrocarbons) andsilicone surfactants. The silicones are typically siloxanes and can bealkoxylated, polyether modified, polyether modified hydroxy functional,amine modified, epoxy modified and other modifications or combinationsthereof. Preferred siloxanes are polymeric, for examplepolydimethylsiloxanes.

In a curable (inkjet) ink a fluorinated or silicone compound may be usedas a surfactant, but preferably a polymerizable surfactant is used.Polymerizable monomers having surface-active effects include siliconemodified acrylates, silicone modified methacrylates, acrylatedsiloxanes, polyether modified acrylic modified siloxanes, fluorinatedacrylates, and fluorinated methacrylates. Polymerizable monomers havingsurface-active effects can be mono-, di-, tri- or higher functional(meth)acrylates or mixtures thereof.

Humectants/Penetrants

Suitable humectants include triacetin, N-methyl-2-pyrrolidone, glycerol,urea, thiourea, ethylene urea, alkyl urea, alkyl thiourea, dialkyl ureaand dialkyl thiourea, diols, including ethanediols, propanediols,propanetriols, butanediols, pentanediols, and hexanediols; glycols,including propylene glycol, polypropylene glycol, ethylene glycol,polyethylene glycol, diethylene glycol, tetraethylene glycol, andmixtures and derivatives thereof. Preferred humectants are triethyleneglycol mono butylether, glycerol and 1,2-hexanediol. The humectant ispreferably added to the inkjet ink formulation in an amount of 0.1 to 40wt % of the formulation, more preferably 0.1 to 10 wt % of theformulation, and most preferably approximately 4.0 to 6.0 wt %.

Preparation of Pigment Dispersions and Inks

Pigment dispersions may be prepared by mixing and/or milling the pigmentin the dispersion medium in the presence of the dispersant.

Mixing apparatuses may include a pressure kneader, an open kneader, aplanetary mixer, a dissolver, and a Dalton Universal Mixer. Suitablemilling and dispersion apparatuses are a ball mill, a pearl mill, acolloid mill, a high-speed disperser, double rollers, a bead mill, apaint conditioner, and triple rollers. The dispersions may also beprepared using ultrasonic energy.

Suitable milling media includes glasses, ceramics, metals, and plastics.In a preferred embodiment, the grinding media can comprise particles,preferably substantially spherical in shape, e.g. beads consistingessentially of a polymeric resin or yttrium stabilized zirconium beads.

Each process in the dispersion process is preferably performed withcooling to prevent build up of heat, and for radiation curable pigmentdispersions as much as possible under light conditions in which actinicradiation has been substantially excluded.

The pigment dispersion may contain more than one pigment. The pigmentdispersion may be prepared using separate dispersions for each pigment,or alternatively several pigments may be mixed and co-milled inpreparing the dispersion.

The dispersion process can be carried out in a continuous, batch orsemi-batch mode.

The preferred amounts and ratios of the ingredients of the mill grindwill vary depending upon the specific materials and the intendedapplications. The contents of the milling mixture comprise the millgrind and the milling media. The mill grind includes pigment, dispersantand a liquid carrier. For (inkjet) inks, the pigment is usually presentin the mill grind at 1 to 50 wt %, excluding the milling media. Theweight ratio of pigment over polymeric dispersant is 20:1 to 1:2.

The milling time can vary widely and depends upon the pigment,mechanical means and residence conditions selected, the initial anddesired final particle size, etc. In a preferred embodiment of thepresent invention pigment dispersions with an average particle size ofless than 100 nm may be prepared.

After milling is completed, the milling media is preferably separatedfrom the milled particulate product (in either a dry or liquiddispersion form) using conventional separation techniques, such as byfiltration, sieving through a mesh screen, and the like. Often the sieveis built into the mill, e.g. a bead mill. The milled pigment concentrateis preferably separated from the milling media by filtration.

In general it is desirable to make (inkjet) inks in the form of aconcentrated mill grind, which is subsequently diluted to theappropriate concentration for use in e.g. the inkjet printing system.This technique permits preparation of a greater quantity of pigmentedink from the equipment. By dilution, the (inkjet) ink is adjusted to thedesired viscosity, surface tension, colour, hue, saturation density, andprint area coverage for the particular application.

Spectral Separation Factor

The spectral separation factor SSF was found to be an excellent measureto characterize a pigmented (inkjet) ink, as it takes into accountproperties related to light-absorption (e.g. wavelength of maximumabsorbance λ_(max), shape of the absorption spectrum andabsorbance-value at λ_(max)) as well as properties related to thedispersion quality and stability.

A measurement of the absorbance at a higher wavelength gives anindication on the shape of the absorption spectrum. The dispersionquality can be evaluated based on the phenomenon of light scatteringinduced by solid particles in solutions. When measured in transmission,light scattering in pigment inks may be detected as an increasedabsorbance at higher wavelengths than the absorbance peak of the actualpigment. The dispersion stability can be evaluated by comparing the SSFbefore and after a heat treatment of e.g. a week at 80° C.

The spectral separation factor SSF of the ink is calculated by using thedata of the recorded spectrum of an ink solution or a jetted image on asubstrate and comparing the maximum absorbance to the absorbance at ahigher reference wavelength λ_(ref). The spectral separation factor iscalculated as the ratio of the maximum absorbance A_(max) over theabsorbance λ_(ref) at a reference wavelength.

${SSF} = \frac{A_{\max}}{A_{ref}}$

The SSF is an excellent tool to design (inkjet) ink sets with largecolour gamut. Often (inkjet) ink sets are now commercialized, whereinthe different inks are not sufficiently matched with each other. Forexample, the combined absorption of all inks does not give a completeabsorption over the whole visible spectrum, e.g. “gaps” exist betweenthe absorption spectra of the colorants. Another problem is that one inkmight be absorbing in the range of another ink. The resulting colourgamut of these (inkjet) ink sets is low or mediocre.

EXAMPLES Materials

All materials used in the following examples were readily available fromstandard sources such as ALDRICH CHEMICAL Co. (Belgium) and ACROS(Belgium) unless otherwise specified. The water used was deionizedwater.

PR122 is Ink Jet Magenta EO2VP2621 which is C.I. Pigment Red 122available from CLARIANT.

PQMIX is Chromophtal™ Magenta 2BC which is a mixed crystal of C.IPugemnt Violet 19 and C.I Pigment Red 202 available from CIBA.PV23 is PV Fast Violet RL which is C.I. Pigment Violet 23 available fromCLARIANT.PO71 is Chromophtal™ DPP Orange TR which is C.I. Pigment Orange 71available from CIBA.PR177 is Chromophtal™ Red A2B which is C.I. Pigment Red 177 availablefrom CIBA.PV19 is the abbreviation for C.I. Pigment Violet 19 for which HostapermRed™ E5BO2 from CLARIANT was used.

DB162 is the polymeric dispersant Disperbyk™ 162 available from BYKCHEMIE GMBH whereof the solvent mixture of2-methoxy-1-methylethylacetate, xylene and n-butylacetate was removed.

S39000 is Solsperse™ 39000 which is a polyethyleneimine core graftedwith polyester-hyperdispersant from LUBRIZOL.

DEGDEE is diethylene glycol diethyl ether.

SYN-1 is a quinacridone dispersion synergist according to formula SYN-1:

The dispersion synergist SYN-1 was prepared as follows.

A RBF was charged with quinacridone PV19 (250 g, 0.8 mol), DMSO (1.6 L)and potassium tert-butoxide (179 g, 1.6 mol) and stirred upon heating to70° C. KI (30 g, 0.18 mol) was added to the mixture which was furtherstirred for 0.5 h at this temperature. Ethylchloroacetate (98 g, 0.8mol) was then added to the solution over a period of 0.5 h via adropping funnel. The mixture was stirred at 70-75° C. for an additional3 h. KOH (135 g, 2.4 mol) was added to the reaction mixture which wasfurther stirred for 1 h at 80° C. prior to the addition of water (0.6 L)and an additional stirring for 0.5 h. At last, HCl 37% (720 g, 6 mol)was carefully added to the solution which was cooled down to roomtemperature, washed with water until reaching pH 4 and dried in a dryoven, at 60° C.

SYN-2 is a quinacridone dispersion synergist prepared according to thesynthesis method disclosed for QAD-3 in paragraphs [0231]-[0233] of WO2007/060259 (AGFA):

SYN-3 is a dispersion synergist according to Formula SYN-3:

58.8 g (0.1 mol) of PV23 was dissolved and heated to 130° C. in 400 mLconcentrate sulphuric acid. After 30 minutes the solution was cooled toroom temperature and dropped into 2 L water. The precipitate wasfiltered off and washed with acetone. The yield of SYN-3 was 85%.

Measurement Methods 1. Measurement of SSF

The spectral separation factor SSF of the ink was calculated by usingthe data of the recorded spectrum of an ink solution and comparing themaximum absorbance to the absorbance at a reference wavelength. Thereference wavelength is dependent on the pigment(s) used:

if the colour ink has a maximum absorbance A_(max) between 400 and 500nm then the absorbance A_(ref) must be determined at a referencewavelength of 600 nm,

If the colour ink has a maximum absorbance A_(max) between 500 and 600nm then the absorbance A_(ref) must be determined at a referencewavelength of 650 nm,

If the colour ink has a maximum absorbance A_(max) between 600 and 700nm then the absorbance A_(ref) must be determined at a referencewavelength of 830 nm. For C.I. Pigment Violet 23 pigments, theabsorbance A_(ref) was determined at a reference wavelength of 730 nm.

The absorbance was determined in transmission with a Shimadzu UV-2101 PCdouble beam-spectrophotometer. The inks were diluted with ethyl acetateto have a pigment concentration of 0.002 wt % based on the total weightof the ink. Quinacridone containing pigments were measured at a dilutionof 0.005 wt % based on the total weight of the ink due to their lowerextinction.

A spectrophotometric measurement of the UV-VIS-NIR absorption spectrumof the diluted ink was performed in transmission-mode with a doublebeam-spectrophotometer using the settings of Table 1. Quartz cells witha path length of 10 mm were used and ethyl acetate was chosen as ablank.

TABLE 1 Mode Absorbance Wavelength range 240-900 nm Slit width 2.0 nmScan interval 1.0 nm Scan speed Fast (1165 nm/min) Detectorphoto-multiplier(UV-VIS)

Efficient pigmented (inkjet) inks exhibiting a narrow absorptionspectrum and a high maximum absorbance have a value for SSF of at least30, more preferably at least 60.

2. Average Particle Size

The particle size of pigment particles in inkjet ink was determined byphoton correlation spectroscopy at a wavelength of 633 nm with a 4 mWHeNe laser on a diluted sample of the inkjet ink. The particle sizeanalyzer used was a Malvern™ nano-S available from Goffin-Meyvis.

The sample was prepared by addition of one drop of ink to a cuvettecontaining 1.5 mL ethyl acetate and mixed until a homogenous sample wasobtained. The measured particle size is the average value of 3consecutive measurements consisting of 6 runs of 20 seconds. For goodink jet characteristics (jetting characteristics and print quality) theaverage particle size of the dispersed particles is below 200 nm,preferably between 70 and 150 nm.

The inkjet ink is considered to be a stable pigment dispersion if theparticle size remained below 200 nm after a heat treatment of 7 days at80° C.

3. Pigment Dispersion Stability

The dispersion stability was evaluated by comparing the SSF before andafter a heat treatment of one week at 80° C. Inkjet inks exhibiting gooddispersion stability have a SSF after heat treatment still larger than30. The % loss in SSF should preferably be as small as possible but isless critical for SSF values larger than 100.

Example 1

This example illustrates the surface modification of the quinacridonepigment C.I. Pigment Red 122.

To a suspension of 5 g PR122 (15 mmol) in 50 mL toluene was added in oneportion 2.4 mL of a 50% aqueous solution of glyoxylic acid (21 mmol).The reaction mixture was heated to reflux and stirred for 16 h. Themixture was allowed to cool down to 20° C. prior to the filtration. Thesolid residue was washed with toluene and acetone, and dried in a dryoven at 70° C. for 24 h. The dry solid PR122-MOD1 was obtained in about80% yield and crushed prior to use for ink dispersion preparation.

Example 2

This example illustrates the surface modification of a mixed crystal oftwo quinacridones, i.e. C.I. Pigment Violet 19 and C.I. Pigment Red 202.

It is believed that the surface modification occurs mainly on C.I.Pigment Violet 19 surface molecules:

To a suspension of 5 g PQMIX (16 mmol) in 60 mL toluene was added in oneportion 2.4 mL of a 50% aqueous solution of glyoxylic acid (21 mmol) and2.5 g of pure CH₃COOH (43 mmol). The reaction mixture was heated toreflux and stirred for 16 h. The mixture was allowed to cool down to 20°C. prior to the filtration. The solid residue PQMIX-MOD1 was washed withtoluene and acetone, and dried in a dry oven at 70° C. for 24 hours. Thedry solid PQMIX-MOD1 was obtained in about 80% yield and crushed priorto use for ink dispersion preparation.

Example 3

This example illustrates different methods for the surface modificationof the diindolotriphenodioxazine pigment C.I. Pigment Violet 23.

First method: to a suspension of 200 g of PV23 (0.34 mol) in 1.4 Ltoluene was added in one portion 20 g of glyoxylic acid in itsmonohydrate form (0.21 mol) and 5 mL HCl 37% (0.06 mol). The reactionmixture was heated to reflux and stirred for 6 h. The mixture wasallowed to cool down to 20° C. and water was then removed throughpartial distillation (about 15% of the reaction's volume). The mixturewas filtrated, washed with toluene and acetone, and dried in a dry ovenat 70° C. for 24 h. The dry solid PV23-MOD1 was obtained in quantitativeyield.

Second method: to a suspension of 200 g of PV23 (200 g, 0.34 mol) in 1.4L toluene was added in one portion 24 mL of a 50% aqueous solution ofglyoxylic acid (0.21 mol) and 5 mL of HCl 37% (0.06 mol). The reactionmixture was heated to reflux and stirred for 6 h. The mixture wasallowed to cool down to 20° C. and water was then removed throughpartial distillation (about 15% of the reaction's volume). The mixturewas filtrated, washed with toluene and acetone, and dried in a dry ovenat 70° C. for 24 h. The dry solid PV23-MOD2 was obtained in quantitativeyield and directly used for ink dispersion preparation.

Third method: to a suspension of 5 g of PV23 (8.5 mmol) in 35 mL toluenewas added in one portion 0.5 g of glyoxylic acid in its monohydrate form(5 mmol) and 0.1 g of MeSO₃H (1 mmol). The reaction mixture was heatedto reflux and stirred for 4 h. The mixture was allowed to cool down to20° C., filtrated and washed with toluene. The solid was dried in a dryoven at 70° C. for 24 h. The dry solid PV23-MOD3 was obtained in about80% yield.

Fourth method: to a suspension of 5 g of PV23 (8.5 mmol) in 35 mLtoluene was added in one portion 0.6 mL of a 50% aqueous solution ofglyoxylic acid (5 mmol) and 0.1 g of MeSO₃H (1 mmol). The reactionmixture was heated to reflux and stirred for 4 h. The mixture wasallowed to cool down to 20° C., filtrated and washed with toluene. Thesolid was dried in a dry oven at 70° C. for 24 h. The dry solidPV23-MOD4 was obtained in about 80% yield.

Example 4

This example illustrates the surface modification of theaminoanthraquinone pigment C.I. Pigment Red 177.

To a suspension of 5 g PR177 (15 mmol) in 50 mL toluene was added in oneportion 1.8 mL of an 50% aqueous solution of glyoxylic acid (15.8 mmol).The reaction mixture was heated to reflux and stirred for 16 h. Themixture was allowed to cool down to 20° C. prior to the filtration. Thesolid residue was washed with toluene and acetone, and dried in a dryoven at 70° C. for 24 h. The dry solid PR177-MOD1 was obtained in about80% yield.

Example 5

This example illustrates different methods for the surface modificationof the diketopyrrolopyrrole pigment C.I. Pigment Orange 71.

First method: to a suspension of 5 g of PO71 (14.8 mmol) in 35 mLtoluene was added in one portion 0.9 g of glyoxylic acid in itsmonohydrate form (8.7 mmol) and 0.1 g of MeSO₃H (1 mmol). The reactionmixture was heated to reflux and stirred for 4 h. The mixture wasallowed to cool down to 20° C., filtrated and washed with toluene. Thesolid was dried in a dry oven at 70° C. for 24 h. The dry solidPO71-MOD1 was obtained in about 80% yield and was directly used for inkdispersion preparation.

Second method: to a suspension of 5 g of PO71 (14.8 mmol) in 35 mLtoluene was added in one portion 1.0 mL of a 50% aqueous solution ofglyoxylic acid (8.7 mmol) and 0.1 g of MeSO₃H (1 mmol). The reactionmixture was heated to reflux and stirred for 4 h. The mixture wasallowed to cool down to 20° C., filtrated and washed with toluene. Thesolid was dried in a dry oven at 70° C. for 24 h. The dry solidPO71-MOD2 was obtained in 80% yield and was directly used for inkdispersion preparation.

Third method: to a suspension of 200 g of PO71 (0.59 mol) in 1.4 Ltoluene was added in one portion 35 g of glyoxylic acid in itsmonohydrate form (0.37 mol) and 5 mL of HCl 37% (0.06 mol). The reactionmixture was heated to reflux and stirred for 6 h. The mixture wasallowed to cool down to 20° C. and water was then removed throughpartial distillation (about 15% of the reaction's volume). The mixturewas filtrated, washed with toluene and acetone, and dried in a dry ovenat 70° C. for 24 h. The dry solid PO71-MOD3 was obtained in quantitativeyield and directly used for ink dispersion preparation.

Fourth method: to a suspension of 200 g of PO71 (0.59 mol) in 1.4 Ltoluene was added in one portion 42 mL of a 50% aqueous solution ofglyoxylic acid (0.37 mol) and 5 mL of HCl 37% (0.06 mol). The reactionmixture was heated to reflux and stirred for 6 h. The mixture wasallowed to cool down to 20° C. and water was then removed throughpartial distillation (about 15% of the reaction's volume). The mixturewas filtrated, washed with toluene and acetone, and dried in a dry ovenat 70° C. for 24 h. The dry solid PO71-MOD4 was obtained in quantitativeyield and directly used for ink dispersion preparation.

Verification of Surface Modification

The efficiency of performing the surface modification was estimated viaa “quick phase coloration test”. Quick phase coloration test procedure:a 0.6 mL sample reaction mixture is put on a porous flagstone so that itcreates a 4 cm diameter circle on it. The residue was then successivelywashed with 2 mL acetone, 2 mL MeOH and 2 mL distillate water. The wetresidue was neither allowed to dry between the successive washing, norafter the last washing step. When the water from the last washing stephad well penetrated the porous flagstone, a test tube (A tube) wascharged with 3 to 5 mg of the wet residue and 5.5 mL distillate water.The mixture of the A tube was ultrasonicated (Sonics Vibra, 60 sec.,maximum power, metal ultrasonicating bar 1.5 cm deep in the tube). To aB tube containing 4 mL of a 0.2% NaHCO₃ solution in water were added 2-3drops of the A tube solution, to reach an 80% optical density at 566 nm.At last, 0.75 mL of CH₂Cl₂ was added to the B tube solution. The B tubewas equipped with a stopper and shacked for 40 seconds (180 Hz, 15 cmamplitude). The B tube was left at rest for phase separation.

Before the surface modification, no coloration of the aqueous phase wasobserved for the pigments PR122, PQMIX, PV23, PO71 and PR177. Aftersurface modification each of the surface modified pigments PR122-MOD1,PQMIX-MOD1, PV23-MOD1 to PV23-MOD4, PO71-MOD1 to PO71-MOD3 andPR177-MOD1 exhibited a coloration of the aqueous phase correspondingwith the colour of the pigment.

Example 6

This example illustrates the dispersion quality and stability of thesurface modified pigments in a non-aqueous inkjet ink based on theorganic solvent DEGDEE.

Preparation and Evaluation of Inkjet Inks

All inkjet inks were prepared in the same manner to obtain a compositionA or B as described in Table 2, depending on whether or not a dispersionsynergist was used.

TABLE 2 wt % of Composition Composition component A B Pigment 5.00 4.50Dispersion 0.50 synergist Polymeric 5.00 5.00 dispersant DEGDEE 90.0090.00

An inkjet ink was made by mixing the pigment, the polymeric dispersant,optionally the dispersion synergist, and the organic solvent DEGDEE witha dissolver and subsequently treating this mixture with a roller millprocedure using yttrium-stabilized zirconium oxide-beads of 0.4 mmdiameter (“high wear resistant zirconia grinding media” from TOSOH Co.).A polyethylene flask of 60 mL was filled to half its volume withgrinding beads and 20 mL of the mixture. The flask was closed with a litand put on the roller mill for three days. The speed was set at 150 rpm.After milling, the dispersion was separated from the beads using afilter cloth.

In accordance with the procedure described in the previous paragraph,the comparative inkjet inks COMP-1 to COMP-11 and the inventive inkjetinks INV-1 to INV-11 were prepared according to Table 3.

TABLE 3 Inkjet Dispersion Polymeric ink Pigment synergist DispersantCOMP-1 PR177 no S39000 COMP-2 PR177 no DB162 COMP-3 PR122 no DB162COMP-4 PR122 SYN-1 DB162 COMP-5 PQMIX no DB162 COMP-6 PQMIX no S39000COMP-7 PQMIX SYN-2 S39000 COMP-8 PO71 no DB162 COMP-9 PV23 no DB162COMP-10 PV23 no S39000 COMP-11 PV23 SYN-3 S39000 INV-1 PR177-MOD noS39000 INV-2 PR177-MOD no DB162 INV-3 PR122-MOD1 no DB162 INV-4PQMIX-MOD1 no DB162 INV-5 PQMIX-MOD1 no S39000 INV-6 PO71-MOD1 no DB162INV-7 PO71-MOD2 no DB162 INV-8 PO71-MOD3 no DB162 INV-9 PO71-MOD4 noDB162 INV-10 PV23-MOD2 no DB162 INV-11 PV23-MOD2 no S39000

The average particle size and the spectral separation factor SSF weredetermined to evaluate the dispersion quality and were determined againafter a heat treatment of 1 week at 80° C. The results are also listedin Table 4.

TABLE 4 Dispersion quality & stability After After heat preparationtreatment Inkjet Size % Loss Size ink SSF (nm) in SSF (nm) COMP-1 5 974 0% 968 COMP-2 14 383  7% 608 COMP-3 22 508  9% 540 COMP-4 96 127 67%324 COMP-5 99 84 67% 242 COMP-6 76 102 55% 227 COMP-7 134 72  4% 74COMP-8 75 204 31% 286 COMP-9 9 1260 Not Not measureable measureableCOMP-10 7 1510 Not Not measureable measureable COMP-11 15 941  0% 357INV-1 63 106  0% 96 INV-2 94 77  0% 74 INV-3 103 96 69% 181 INV-4 130 54 5% 54 INV-5 118 71 13% 70 INV-6 187 76 45% 114 INV-7 152 77  0% 73INV-8 300 73 19% 68 INV-9 178 72  0% 73 INV-10 157 90 30% 90 INV-11 12194 16% 98

From Table 4, it should be clear that inkjet inks INV-1 to INV-11 usingsurface modified pigments exhibited improved dispersion quality andstability. For none of these inks, a particle size larger than 200 nmwas observed after heat treatment, which is important to guaranteecontinuous printing without production loss due to nozzle or enginefailures.

Although a substantial loss in SSF was observed for the quinacridonepigment PR122 in inkjet ink INV-3, there was no gelation or flocculationobserved as was the case for the comparative inks COMP-3 and COMP-4. Forthe comparative inks COMP-9 and COMP-10, the flocculation was even sosevere that measurement of SSF and average particle size becameimpossible.

The good results of comparative inkjet ink COMP-7 are due to theaddition of a dispersion synergist having a certain molecular similaritywith the pigment PQMIX. This development of a specific dispersionsynergist for each pigment class leads to high additional cost and iseconomically less attractive.

Example 7

This example illustrates the compatability of the surface modifiedorganic pigments according to the present invention with polymerizablecompounds having at least one vinyl ether group in electron beam curableinkjet inks.

Preparation of Sulfonated Pigment SPV23

A mixture of 50 g of the pigment PV23, 380 mL acetonitrile and 2.5 gsulfuric acid is placed in a vessel open only at the top. This vessel isconnected to a Liebig condenser and the mixture is refluxed for 8 hoursat 80° C. reaction temperature. The mixture is then cooled to 20° C. andfiltered. The filtrate was washed with water until a pH of 5 was reachedby the filtrate. The filtrate was dried overnight at 40° C. in a vacuumoven. 47 g of a violet powder of the pigment SPV23 were recovered.

Preparation and Evaluation of Inkjet Inks

The inkjet inks COMP-12, INV-12 and INV-13 were prepared in the samemanner to obtain a composition as described in Table 5.

TABLE 5 wt % of component Comp-12 INV-12 INV-13 Sulfonated Pigment SPV235.00 — — Carboxylated pigment PV23-MOD1 — 5.00 — Carboxylated pigmentPV23-MOD3 — 5.00 Polymeric dispersant DB162 5.00 5.00 5.00 VEEA 90.00 90.00  90.00 

An inkjet ink was made by mixing the pigment, the polymeric dispersantDB162 and the polymerizable monomer VEEA with a dissolver andsubsequently treating this mixture with a roller mill procedure usingyttrium-stabilized zirconium oxide-beads of 0.4 mm diameter (“high wearresistant zirconia grinding media” from TOSOH Co.). A polyethylene flaskof 60 mL was filled to half its volume with grinding beads and 20 mL ofthe mixture. The flask was closed with a lit and put on the roller millfor three days. The speed was set at 150 rpm. After milling, thedispersion was separated from the beads using a filter cloth

The average particle size and the spectral separation factor SSF weredetermined to evaluate the dispersion quality and were determined againafter a heat treatment of 1 week at 60° C. The results are shown inTable 6.

TABLE 6 Dispersion quality & stability After After heat preparationtreatment Inkjet Size Size ink SSF (nm) SSF (nm) COMP-12 32 108Flocculated INV-12 59 96 57 98 INV-13 77 107 71 104

On mixing the components of the comparative inkjet ink COMP-12, a largetemperature increase was observed, which is believed to be indicativefor reaction with the vinylether group of VEEA. After a milder heattreatment of 1 week at only 60° C., complete flocculation and largeagglomerates were observed for the comparative inkjet ink COMP-12. Table6 shows that the heat treatment had no effect on the excellentdispersion quality of the inventive inkjet inks INV-12 and INV-13

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1-15. (canceled)
 16. A method for preparing a surface modified organicpigment, the method comprising the steps of: reacting an organic pigmentin an aromatic hydrocarbon solvent with a surface modifying reagent toform the surface modified organic pigment; and washing and drying thesurface modified organic pigment; wherein the surface modifying reagentis represented by Formula (I):

X is selected from the group consisting of O, S, and N—R3; Y is selectedfrom the group consisting of O and NR4; R1 to R4 are each independentlyselected from the group consisting of hydrogen, an alkyl group, analkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, andan aryl group and a heteroaryl group; and when Y—R1 is different fromOH, at least one of R2 to R4 is substituted by at least one functionalgroup having a pKa between 2.5 and
 9. 17. The method according to claim16, wherein the surface modifying reagent is represented by Formula(II):

wherein R2 is defined in Formula (I).
 18. The method according to claim16, wherein X represents O.
 19. The method according to claim 16,wherein R2 is selected from the group consisting of hydrogen, an alkylgroup, and an aryl group.
 20. The method according to claim 16, whereinthe surface modifying reagent is selected from the group consisting ofglyoxylic acid, pyruvic acid, 2-oxobutanoic acid, and phenyl glyoxylicacid.
 21. The method according to claim 16, wherein the organic pigmentis selected from the group consisting of quinacridone pigments,diketopyrrolopyrrole pigments, quinolonoquinolone pigments, dioxazinepigments, aminoanthraquinone pigments, indanthrone pigments,bisbenzimidazobenzophenanthroline dione pigments, and mixed crystalsthereof.
 22. A surface modified organic pigment comprising: at least onefunctional group according to Formula (I) attached to its surface:

wherein the dashed line in Formula I represents a covalent bond to onepigment molecule at a pigment surface; X is selected from the groupconsisting of OR5, SR6, NR3R7, and a halogen; Y is selected from thegroup consisting of O and NR4; R1 to R4 are independently selected fromthe group consisting of hydrogen, an alkyl group, an alkenyl group, analkynyl group, an aralkyl group, an alkaryl group, an aryl group, and aheteroaryl group; R5 to R7 are independently selected from the groupconsisting of hydrogen, an alkyl group, an alkenyl group, an alkynylgroup, an aralkyl group, an alkaryl group, an aryl group, and aheteroaryl group and an acyl group; any one of R1 to R7 may representnecessary atoms to form a five to eight membered ring with one of theother groups selected from R1 to R7; and when Y—R1 is different from OH,at least one of R2 to R7 is substituted by at least one functional grouphaving a pKa between 2.5 and
 9. 23. The surface modified organic pigmentaccording to claim 22, wherein Y represents O, and R1 is hydrogen. 24.The surface modified organic pigment according to claim 22, wherein X isa hydroxyl group.
 25. The surface modified organic pigment according toclaim 22, wherein R2 is selected from the group consisting of hydrogen,an alkyl group, and an aryl group.
 26. The surface modified organicpigment according to claim 22, wherein the one of pigment molecule atthe pigment surface is selected from the group consisting ofquinacridone, diketopyrrolopyrrole, quinolonoquinolone, dioxazine,aminoanthraquinone, indanthrone, and bisbenzimidazobenzophenanthrolinedione.
 27. A non-aqueous ink containing a surface modified organicpigment according to claim
 22. 28. The non-aqueous ink according toclaim 27, wherein the non-aqueous ink is a radiation curable ink. 29.The non-aqueous ink according to claim 28, further comprising apolymerizable compound including at least one vinyl ether group that isa vinyl ether acrylate.
 30. The non-aqueous ink claim 27, wherein thenon-aqueous ink is a non-aqueous inkjet ink.